This application is in response to the NIH Program Announcement entitled "Innovative grant program for AIDS vaccine research " through the R21 mechanism. The AIDS virus, HIV, has been spreading continuously worldwide. One of the difficulties in developing an effective vaccine lies in the mucosal transmission of the virus. Currently, neither conventional vaccines nor oral vaccines are sufficient to induce mucosal immunity in the vagina. Therefore, the objective of this study is to develop a bacterial vector-based vaccine capable of vaginal delivery. With a NIH small grant, we have successfully established a gene-cloning system and selected a gene-expression cassette for both extracellular and surface-bound expression of foreign antigens in human vaginal lactobacilli. We hypothesize that vaginal lactobacilli can be engineered to deliver HIV vaccines. We propose to achieve two specific aims: 1) clone HIV envelope antigens (gp120 and gp41) into vaginal lactobacilli and express them both on the cell surface and as freely secreted peptides, and 2) evaluate the expression of recombinant HIV antigens by in vitro antibody assays and by in vivo induction of mucosal immunity in animals. We expect to document the feasibility of using lactobacilli to deliver HIV antigens to the vaginal tract. This study will be the important next step of our initial NIH small grant project. It will also be essential to attaining our long-term goal of developing a safe and effective mucosal vaccine to protect women against sexual HIV transmission.